This invention relates to the art of electronic signal filtering, and more particularly, to multi-stage spectral translation by alternate modulation and demodulation of an incurrent signal.
In presently available variable cutoff frequency electronic filters, the cutoff frequency is typically set by linear components, and is therefore limited by the accuracy of those components, usually plus or minus five percent. The attenuation of the stopband in these filters is basically proportional to either the frequency raised to some power if the filter is a low-pass design, or the inverse of the frequency raised to some power if it is a high pass design. Additionally, passband attenuation and ripple near the cutoff frequency, often on the order of 3dB, hinders performance.